Aug 23, 2015
The night I caught Rosetta's comet

Sen—I have written many times about Europe’s inspiring Rosetta mission which is currently studying a comet like never before. I was lucky enough to be at mission control at Darmstadt, Germany, on the exciting day when its little lander Philae bounced to that extraordinary, if unexpected, landing on the surface of 67P/Churyumov-Gerasimenko. I have got to know a number of scientists working on the project, but recognised that as a journalist, my part would be to remain simply a fascinated observer.

However, this week I managed to achieve my own little first when I got to locate Comet 67P for myself. With a fairly basic telescope and my very ordinary digital SLR camera, I was able to take an image of the comet from my seaside home.

Now I don’t expect my simple set-up to add any significant information to the data being gathered by the Rosetta experts. It is no OSIRIS, for sure, and I was observing from a lot further away! My image shows the comet as just a faint splodge in a field of distorted stars, but the fact I captured it at all gave me quite a buzz.

I was especially pleased because I don’t have any previous experience of photographing stars through a telescope, unless you consider that all camera lenses are a form of telescope. Over many years I have dabbled with taking shots of the night sky with simply a camera and a normal lens. If you’re talking stars, then time exposures are always necessary, but most consumer-standard SLR cameras nowadays will allow an exposure long enough to record them.

With a standard lens, such as came with your camera, you will find that if you leave the shutter open for longer than about 20 seconds, then the stars will begin to show as short lines rather than points of light. These so-called “star trails” are clear evidence that we are inhabiting a rotating planet. The stars cross the sky just as we see the Sun rise and set each day.

I have often recorded star trails with a camera on a simple tripod. I’ve also piggybacked the camera on telescope mounts, and even a basic home-made contraption called a scotch or barndoor mount, to counter the Earth’s rotation and take time exposures that stop the stars from trailing. Such set-ups have allowed me not just to take photos of familiar constellations, but also to capture meteors or “shooting stars”. On rare occasions, I have also photographed comets with this equipment, but only because these were comets bright enough to be seen with the naked eye, including Halley’s Comet in 1986, Hale-Bopp in 1997, and Lovejoy at the end of last year.

It may not look terribly impressive, but the faint splodge indicated by the yellow lines is Comet 67P, imaged by the writer. Image credit: Paul Sutherland

What I have never done is try for the really faint stuff. I’ve been happy to leave such endeavours to highly-advanced amateurs using big telescopes with highly stable mounting systems that cost an arm and a leg, plus dedicated astronomical CCD cameras, with appropriate software. These powerful systems, combined with the skill of their users, allows them to produce results of a professional standard.

The Rosetta team recognised the abilities of this band of amateur astronomers—where amateur is accorded its original meaning as a lover of a subject, rather than something of a bodger—and set up a section to coordinate the results. Its leader, Padma Yanamandra-Fisher, told Sen earlier this year that the campaign would allow Rosetta scientists to get a new perspective on Comet 67P and to compare its appearance from afar with the results being achieved by the orbiter.

I was keen to see what the chances were of ordinary stargazers getting a glimpse of the comet when at its brightest, around perihelion. It turned out that conditions are far from ideal on this visit to the inner Solar System. The comet is currently in the constellation of Gemini which doesn’t rise until the early hours, and then remains fairly low in the sky before pre-dawn twilight begins. On top of that, the comet is on the far side of the Sun this time round and so isn’t getting particularly bright. It was predicted to get to around magnitude 12 at best, which is a couple of hundred times fainter that the faintest star the human eye can see on a clear, dark night!

As it happens, I had bought a new telescope just a few weeks ago. A portable 66mm (2.5-inch) refractor that I would be able to use as a spotting scope, take to eclipses, and which would make a very useful 400mm lens for my Canon EOS 600D camera too. It is a lovely, solid piece of kit and I dared to wonder whether it might be enough to catch me Comet 67P.

Though the comet’s location in the sky is not ideal for many, I was better placed than most. My seaside apartment’s balcony on the Kent coast in the UK gives me a clear and dark view to the east, over the sea, with nothing between me and Belgium!

Trusting my ancient mount’s drive, I took 25 one-minute exposures at a fast camera speed of 3200 ISO, on the morning of August 22, and hoped for the best. Later in the day, I stacked them—a process that builds up the collected light and improves contrast—and looked for the comet. The mount didn’t track the stars quite as perfectly as I’d have liked, but there was a tiny smudge in exactly the right place amongst them. I was elated. For although I may have nothing more than misshapen stars and a faint splodge, I felt thrilled to have caught Rosetta’s comet for myself!